The present invention relates to display devices with integrated beam forming lens-lets or micro-lenses. More particularly, the present invention relates to the use of solid state emissive display devices with small lenses placed on or integrated into the display device substrate and associated with each light emitting element or sub-element.
Digital imaging devices are widely known and used in electronic equipment. Solid-state imaging devices, those which are constructed on a substrate which may contain integrated drive circuitry, are very useful for portable imaging applications in which a light, rugged, high-quality display is needed. Such devices often rely on liquid crystal displays or light emitting diodes. In particular, organic light emitting diodes (OLEDs) provide a very thin, high-quality, and low-power technology for color image display with Lambertian emission characteristics providing a wide viewing angle. The OLED technology can be built upon a glass substrate as well as traditional silicon wafers.
Such displays, in general, are capable of reproducing images by writing specific information to a plurality of light emitting elements on a surface. These light emitting elements are generally organized as a rectangular array and are addressed via control lines connected to the display device. Each light emitting element is individually addressable and specific data values representing an amount of light to be produced, can be written to them; each data value then being expressed as an element in the displayed image. For color displays, each light emitting element is generally composed of sub-elements in each of several, usually three, primary colorsxe2x80x94typically red, green, and blue. Since the sub-elements are so small, a human observer will see the additive combination of the primary colors enabling the display of many different colors. Each of these sub-elements elements is individually addressable by the control and data lines of the display device.
Optical technology has now progressed to the point that very small optical elements can be created. These elements can be fabricated in a variety of ways and can be combined into an array of small elements covering a surface. Each lens element affects the light passing through according to that element""s surface profile and its refractive index. The lens element is referred to as a lens-let, micro-lens-let, or micro-lens or in the case of periodic cylindrical lenses: lenticular arrays. This technique of optical design differs from the traditional in that different portions of a beam can be made to pass through different optical elements, enabling a variety of effects. The construction of the lens-lets on a surface also enables the implementation of optical effects using smaller optical elements because each lens-let is very small and the surface on which they are made can be very thin and light-weight. It is also the case that construction techniques for lens-let arrays has progressed to the point that such arrays are well understood and manufacturable (see U.S. Pat. No. 5,867,321, issued Feb. 2, 1999 to Nakama et al., entitled Planar Microlens Array and Method of Making Same). Hence, thin, robust, imaging systems with a wide variety of properties can be created using this technology.
Digital imaging displays have been integrated with micro-lens technology to improve the optical characteristics of the display. Most such implementations rely on laminating a micro-lens array on the surface of a display device. In particular, some liquid crystal display devices include a micro-lens layer to shape the light entering and exiting from each light emitting element in the display so as to improve the viewing angle of the display or otherwise enhance the display characteristics (see EP 0 640 850 A2, published Mac. 1, 1995, Suzuki et al., entitled Microlens Array Sheet for a Liquid Crystal Display, Method for Attaching the Same and Liquid Crystal Display Equipped with the Same; U.S. Pat. No. 5,680,186, issued Oct. 21, 1997 to Watanabe et al., entitled Liquid Crystal Display Device with Microlenses Having a Focal Point Between a Cover Layer and the Liquid Crystal Layer""s Center; and EP 0 615 150 A3 and A2, published Sep. 9, 1994, Borrelli et al., entitled Cover Glass for LCD Panel). It is also possible to integrate a micro-lens directly upon a substrate of display light emitting elements with the use of resins to form the lenses (see EP 0 658 779 A2, published Jun. 21, 1995, Mizuguchi et al., entitled Microlens Substrate). In the first case, a separate substrate or layer must be incorporated into the device, adding manufacturing cost and difficulty. In the second case, the integration of resin materials on a substrate is problematic from both a materials and process perspective. In both cases, the designs are for liquid crystal devices.
Other integrations of light emitting devices and microlenses have also been explored. For example, EP 0 384 849 B1, published Aug. 29, 1980, Shimada et al., entitled A Semiconductor Light Emitting System describes an LED with an integrated micro-lens on the same substrate which radiates parallel to the substrate. Such designs are not suitable for a multi-element display device and require complex photolithography techniques. Micro-lenses are also used in conjunction with solid-state light capturing devices (see EP 0 744 778B1, published Nov. 27, 1996, Sano et al., entitled Solid-State Imaging Device and Method of Manufacturing the Same) and in light-valve displays (U.S. Pat. No. 5,757,124, issued May 26, 1998 to E. Pope, entitled Display Screen Having Amorphous Silica Microspheres with Fluorescence Behavior) using masks and micro-spheres. Cathode ray tubes with a layer of light emitting element level optical micro-lenses are also known (EP 0 957 385 A1, published Nov. 17, 1999, S. Zelitt, entitled 3-D Imaging System) in this case to support three-dimensional (3-D) imaging.
These techniques rely on the use of an additional surface with micro-lenses attached to the surface of a digital image display, the use of a special cover material surface with micro-lenses encapsulating the display, or special process methods to integrate micro-lenses on the base substrate. In the first case, additional materials, components, and process steps are needed to fabricate a solid-state display with micro-optical components. In the second case an existing component must be specially treated and aligned with the other components and, in the third case, difficult materials and non-standard process methodologies must be undertaken which limits the use of the technique. Moreover, many of these methods are limited in application to liquid crystal display devices.
Hence, digital image display systems that are portable, small, and lightweight, are greatly restricted in their ability to integrate optical elements for producing desirable effects. When added to an imaging system, the optical elements are too bulky, lack robustness, or require manufacturing methods and precision, which adds to the cost of the system.
In standard emissive OLED devices the energy is emitted uniformly in all directions. This is an advantage over LCD displays, which are more directional. The disadvantage of this uniform angular emission is that much energy is used for directions that, in many applications, are not useful. It would be desirable to direct the emission directly at the user and spare the energy currently employed away from the user. Another advantage for this would be for security so that other users could not view the screen.
There is a need therefore to provide an improved display that directs the energy to an observer and spares the energy required to transmit to regions away from the viewer.
The need is met according to the present invention by providing an image display device that includes a substrate; a sparse array of light emitting elements formed on one side of the transparent substrate, the light emitting element being selectively addressable to form an image; an array of lens-lets located on the opposite side of the substrate, the focal plane of the lens-lets being at the one side of the substrate and the lens-lets being arranged with respect to the light emitting elements such that the light emitted by the light emitting elements is directed by the respective lens-lets to intersect at a common region associated with a predetermined viewing distance; and the sparseness of the array of the light emitting elements being such that the ratio of the light emitting area of the light-emitting element under a lens-let to the total area of the lens-let is less than or equal to 0.25.
The present invention has the advantage of providing a low-cost, small, and energy efficient display. Another advantage is that the viewer of the display has improved privacy for the subject matter being viewed.